The present invention relates to a method and a device for driving an arrangement that delivers a pressurized medium in a vehicle brake system to adjust an available volume of pressurized medium.
The German Published Patent Application No. 44 40 517 describes a method and a device for driving a return pump of a brake system, where the return pump is able to be controlled as a function of the manipulated variable and/or of the system deviation of a slip controller and/or of a governor that is able to influence the driving speed of a vehicle. In this context, for example, a vehicle speed governor or a vehicle speed limiter transmits a signal to an ABS/ASR system which indicates a desired brake application and/or a desired braking torque. An appropriate signal, which indicates a brake application, can also be supplied by other systems, for example by a vehicle dynamics control. Such systems now provide for the pressure buildup to be defined by way of the pump motor in response to an active brake application, the return pump being driven as a function of demand during the pressure buildup. The result is that the return pump is driven during the brake application that is active at the moment, as a function of the system deviation of a governor which influences the braking torque and/or the wheel speed.
The related art is not able to provide optimal results in every respect. It is precisely a brake application at a higher vehicle velocity, for example with ABS control, that leads to a distinctly greater volumetric consumption than at a lower vehicle velocity. Thus, at a very high volumetric consumption of the pressurized medium, safety can be jeopardized by an insufficient volume in the brake circuit and by a pump that is delivering too slowly. Thus, the objective to be fulfilled is to devise a method and device which will make it possible for a sufficient volume of pressurized medium to be available at all times in a vehicle""s brake system, and, in the process, will enhance safety. The aim is to achieve this objective with the simplest possible implementation.
The method and device according to the present invention make it possible to advantageously avoid a situation, for example, where there is insufficient pressurized medium volume during a brake application, in spite of the arrangement delivering the pressurized medium being driven to a maximum. This is achieved by setting up a relationship between the pressurized medium volume available in at least one brake circuit, which depends on the driving of the arrangement delivering the pressurized medium, and the vehicle speed. This entails driving the arrangement delivering the pressurized medium as a function of the vehicle speed so as to effectively correlate the vehicle speed and the pressurized medium volume available in the brake circuit.
The vehicle speed and the pressurized medium volume available in the brake circuit are correlated to effect that with rising vehicle speed, the available volume of pressurized medium in the brake circuit is increased, and/or with falling vehicle speed, the available volume of pressurized medium in the brake circuit is decreased.
In one advantageous refinement, the pressurized medium volume available in the brake circuit is adjusted in a storage device in communication with the brake circuit by the pressurized medium volume contained therein and, in fact, in such a way that the pressurized medium volume in the storage device is increased in response to rising vehicle speed, and/or lowered in response to falling vehicle speed.
In the process, a pressure quantity prevailing in the brake system is advantageously determined, which can be used to determine and/or adjust the available volume of pressurized medium.
Also beneficial is that the driving of the arrangement delivering the pressurized medium is activated or deactivated as a function of at least one predefinable threshold value of the pressure quantity, the threshold value being expediently predefined and/or adjusted in a dependency ratio to the vehicle speed.
In one advantageous refinement, the driving of the arrangement delivering the pressurized medium is activated or deactivated as a function of the pressure quantity in such a way that in response to a first pressure-quantity threshold value being reached and/or not attained, the driving is activated, and, in response to a second pressure-quantity threshold value being reached and/or exceeded, the driving is deactivated. The enable, i.e., disable limits of this hysteresis are thus expediently varied as a function of the vehicle speed in such a way that the available pressurized medium volume also suffices in consideration of safety aspects.
Also beneficial is that the dependency ratio between pressurized medium volumes and vehicle speed can be so formulated that, from a comparison of the vehicle speed to speed threshold values, vehicle-speed ranges can be predefined, and threshold values for the pressure quantity can be preset in each of these ranges. In the same way, the dependency ratio can advantageously be so conceived that the particular threshold values for the pressure quantity can be allocated to the vehicle""s speed by a characteristic curve or a characteristics map. In the same way, the dependency ratio can advantageously be predefined or adjusted as a linear relation, in particular as a proportional relation, between the vehicle speed and threshold values of the pressure quantity.
Thus, by shifting the hysteresis of the closed-loop control of the arrangement delivering the pressurized medium as a function of the vehicle speed, a greater volume of pressurized medium is made available at the beginning of a brake action, in particular in the storage device of an electrohydraulic brake system, thereby assuring that, in spite of a heavy volumetric consumption of pressurized medium, a sufficient volume of pressurized medium is always present, in particular in the storage device.